This is the same problem that happened to me in 20H1 update. I was told it was an issue with certain NVidia cards. When I searched the internet, all the solutions I found did not work. Finally, I found one that said, "I disable all the sleep items of the NIC properties window" and that also fixed my issue as well. Now, with 21H1, the same problem is back again. But, my NIC already have those sleep items disabled. So, that isn't the solution to the 21H1 update.
Whatever the problem is, it is basically disabling the NVidia card somehow, even though the card says it is working. If I disable the card, things seem to get close to normal operating speeds. However, with the card disabled, games, etc that relied on the gpu of the NVidia card are slow, low frame rates, etc.
In my case, I disabled the NVidia card. Intel GPU has the game running under 20 FPS. With NVidia enabled, game stayed around 25-30 fps in normal environment. And clear to me the NVidia card is not running properly, because normally, at the normal 60 fps I set it for, the system heats up to the touch, where the card is. But, after the update, no heat up, even though the card is "working".
I am hoping someone would read this and a possible idea of a solution would pop into their head.